Fix printf formatting on MacOS

[graetzer]

On MacOS with clang the compilation of tools/db_bench_tool.cc always fails because the format used in a fprintf call has the wrong type. This PR should hopefully fix this issue

tools/db_bench_tool.cc:4233:61: error: format specifies type 'unsigned long long' but the argument has type 'size_t' (aka 'unsigned long')

[maysamyabandeh]

Thanks @graetzer There might be more of such issues. Can you apply this patch to the PR so that i) we prevent such mistakes in future ii) we find and fix if there is any other issues in tools built under mac.

--- a/.travis.yml
+++ b/.travis.yml
@@ -90,7 +90,7 @@ script:
       OPT=-DTRAVIS V=1 ROCKSDBTESTS_START=db_block_cache_test ROCKSDBTESTS_END=full_filter_block_test make -j4 check_some
       ;;
     2)
-      OPT=-DTRAVIS V=1 ROCKSDBTESTS_START=full_filter_block_test ROCKSDBTESTS_END=write_batch_with_index_test make -j4 check_some
+      OPT=-DTRAVIS V=1 make -j4 tools && OPT=-DTRAVIS V=1 ROCKSDBTESTS_START=full_filter_block_test ROCKSDBTESTS_END=write_batch_with_index_test make -j4 check_some
       ;;
     3)
       OPT=-DTRAVIS V=1 ROCKSDBTESTS_START=write_batch_with_index_test ROCKSDBTESTS_END=write_prepared_transaction_test make -j4 check_some

[maysamyabandeh]

A kind reminder.

[graetzer]

ok did that

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